Power generation using natural energy, such as wind-power generation and solar power generation, is affected by weather conditions and sometimes results in unstable outputs. Thus, there is a need to level out outputs by using an energy storage system such as a CAES (compressed air energy storage) system.
A conventional CAES (compressed air energy storage) power generation device generally stores electric energy as compressed air during off-peak hours at a power plant and generates electric energy during high power demand hours by driving an expander using the compressed air and operating a generator.
Such a CAES power generation device using natural energy is disclosed, for example, in Patent Document 1 and Patent Document 2.
Patent Document 1 discloses a CAES power generation device using wind power.
Patent Document 2 discloses a CAES power generation device using solar light.
Power generation using natural energy causes a long-period and short-period output variations. The terms “long-period” and “short-period” are not clearly defined, however the long-period variation takes place in about several hours to several days. On the other hand, the short-period variation takes place in about several minutes to less than an hour. For example, in power generation using solar light, the long-period output variation is caused by a difference between the daytime and the night. The short-period output variation is caused when the sun temporarily disappears behind a cloud. On the other hand, in power generation using wind power, the long-period output variation is caused when power generation is stopped by strong wind or a windless condition, while the short-period output variation is caused by fluctuations in wind velocity.
The conventional CAES power generation devices using natural energy, including the ones disclosed in Patent Document 1 and Patent Document 2, comprise a compressed air storage tank having a large capacity, and store compressed air when power demand is low and generate power by the stored compressed air when power demand is high. However, the tank having a large capacity takes a long time, in starting, to be pressurized to a level suitable for generating power after the compression is started, and is thus not suitable for leveling out the short-period output variation.